Regional changes in corneal thickness and shape with soft contact lenses.

PURPOSE

To investigate the influence of soft contact lenses on regional variations in corneal thickness and shape while taking account of natural diurnal variations in these corneal parameters.

METHODS

Twelve young, healthy subjects wore four different types of soft contact lenses on four different days. The lenses were of two different materials (silicone hydrogel or hydrogel), designs (spherical or toric), and powers (3.00 or -7.00 diopter). Corneal thickness and topography measurements were taken before and after 8 h of lens wear and on 2 days without lens wear, using the Pentacam HR system. RESULTS.: The hydrogel toric contact lens caused the greatest level of corneal thickening in the central (20.3 +/- 10.0 microm) and peripheral cornea (24.1 +/- 9.1 microm) (p < 0.001) with an obvious regional swelling of the cornea beneath the stabilizing zones. The anterior corneal surface generally showed slight flattening. All contact lenses resulted in central posterior corneal steepening, and this was weakly correlated with central corneal swelling (p = 0.03) and peripheral corneal swelling (p = 0.01).

CONCLUSIONS

There was an obvious regional corneal swelling apparent after wear of the hydrogel soft toric lenses because of the location of the thicker stabilization zones of the toric lenses. However, with the exception of the hydrogel toric lens, the magnitude of corneal swelling induced by the contact lenses over the 8 h of wear was less than the natural diurnal thinning of the cornea over this same period.